1. Field of the Invention
The present invention relates to a communication technique for synchronously transmitting data from a single signal source to multi-channel playback devices.
2. Description of the Related Art
A multi-channel speaker system (to be abbreviated as “multi-CH SP system” hereinafter) as the prior art is used together with a digital television, DVD player, AV amplifier, and the like to form a home theater. A wiring example of a typical home theater has an arrangement shown in FIG. 20. Reference numeral 2001 denotes a digital television (to be abbreviated as “DTV” hereinafter); reference numeral 2002, a DVD player (to be abbreviated as “DVD” hereinafter); reference numeral 2003, an audio video amplifier (to be abbreviated as “AV amplifier” hereinafter); and reference numerals 2004 to 2009, six speakers (SPs) which form a 5.1CH surround system. For example, reference numeral 2004 denotes a subwoofer (to be abbreviated as “SW” hereinafter); reference numeral 2005, a center SP; reference numeral 2006, an L-channel main SP; reference numeral 2007, an R-channel main SP; reference numeral 2008, an L-channel rear SP; and reference numeral 2009, an R-channel rear SP.
As for the wiring among these devices, reference numeral 2030 denotes a wiring line which connects the AV amplifier 2003 and DTV 2001. Typically, the wiring line 2030 comprises an HDMI cable used to connect the HDMI output of the AV amplifier 2003 to the HDMI input of the DTV 2001. Reference numeral 2031 denotes an HDMI cable which connects the HDMI output of the DVD 2002 to the HDMI input of the AV amplifier 2003, typically. Reference numerals 2032 to 2037 denote SP cables connected from the AV amplifier 2003 to the six SPs, respectively. On the other hand, as for power supply wiring, reference numeral 2040 denotes an AC power supply line of the DTV 2001; reference numeral 2041, a power supply line of the DVD; and reference numeral 2042, a power supply line of the AV amplifier.
FIG. 20 is a block diagram showing the prior art of full wired wiring using analog speaker cables. In this case, the SPs are wired by six SP cables from the AV amplifier. These SP cables impose a heavy load on the user since they must be wired in consideration of the plus and minus polarities, R and L (right and left) channel differences, and the like.
How to simplify many, complicated SP wiring lines from the AV amplifier is the first issue (wiring simplification).
The second issue (digitization) of the present invention is to prevent performance degradation due to analog connection. In particular, since the wiring line length to each rear speaker is long, the rear speaker is vulnerable to performance degradation due to the resistance of the connected SP cable.
Furthermore, the following problem potentially exists. That is, since it is difficult for the user to notice that any wiring line is disconnected from a corresponding speaker, he/she may be unaware that the fidelity of a playback sound is, in fact, lost. It is possible to improve the convenience by notifying the user of the status of each speaker such as status information indicating, for example, a standby status or conditions including a failure. That is, the third issue is to make it possible to grasp and control the status of each speaker on the control side such as the AV amplifier side.
As a method of solving the first to third issues, a method of connecting a playback audio signal from an optical disk player to playback devices including SPs by, for example, IEEE1394 via a network has been proposed, as described in Japanese Patent Laid-Open Nos. 2001-223588 and 2002-217911.
Also, Japanese Patent Laid-Open Nos. 2005-198249, 2005-175744, and 2005-175745 disclose a surround system by means of a wired bus-connected network system. As an example of the bus-connected network, USB, IEEE1394, and the like are known.
However, these methods pose the following new problems.
(1) Each SP requires a power supply. However, the power consumption of the surround system is around 100 W per CH, and such electrical power cannot be supplied via a USB (DC 5 V, 0.5 A) or IEEE1394 (DC 8 to 40 V, 1.5 A) connection cable. For this reason, each SP must individually receive a power supply. Then, as the prior art of network wiring using IEEE1394 (1394 wiring), the actual wiring state including power supplies becomes as shown in FIG. 21, resulting in troublesome power supply wiring. Referring to FIG. 21, reference numerals 2140 to 2145 denote power supply wiring lines to be newly added.
(2) The cable length must be limited to about 5 m, and the cable is relatively expensive since it adopts a multi-core structure.
(3) To support the transmission protocol, each device such as the SP must incorporate an advanced-function CPU, resulting in an expensive system.
(4) As the audio signal playback requirement for the surround system, playback time management is required. For example, in the case of IEEE1394, such management is achieved using time stamps included in its isochronous data packets. That is, each device holds synchronized clocks, and controls the output timing of playback data based on time stamp information included in incoming received data. Also, hardware for this purpose becomes relatively expensive.
(5) Since IEEE1394 or the like is a standard I/F, if it is used in the surround system, an unexpected device is likely to be connected, and an extra processing function must be equipped to cope with errors.